Rabies is a disease that can occur in all warm-blooded species and is caused by rabies virus. Infection with rabies virus followed by the outbreak of the clinical features in nearly all instances results in death of the infected species. In Europe, the USA and Canada wild life rabies still exists and is an important factor in the cause of most human rabies cases that occur. On the other hand, urban rabies constitutes the major cause of human rabies in developing countries. In fact, more than three billion people in Asia and Africa are at high risk of contracting rabies and fifty thousand die of the disease each year. Virtually all of these human cases occur in developing countries as the result of exposure to rabid dogs. For this reason, there is an urgent need for more effective rabies vaccination of community dogs in these countries.
Rabies virus is a non-segmented negative-stranded RNA virus of the Rhabdoviridae family. Rabies virus virions are composed of two major structural components: a nucleocapsid or ribonucleoprotein (RNP), and an envelope in the form of a bilayer membrane surrounding the RNP core. The infectious component of all Rhabdoviruses is the RNP core which consists of the RNA genome encapsidated by the nucleocapsid (N) protein in combination with two minor proteins, i.e. RNA-dependent RNA-polymerase (L) and phosphoprotein (P). The membrane surrounding the RNP core consists of two proteins: a trans-membrane glycoprotein (G) and a matrix (M) protein located at the inner site of the membrane. The G protein, also referred to as spike protein, is responsible for cell attachment and membrane fusion in rabies virus and additionally is the main target for the host immune system. The amino acid region at position 330 to 340 (referred to as antigenic site III) of the G protein has been identified to be responsible for the virulence of the virus, in particular the Arg residue at position 333. All rabies virus strains have this virulence determining antigenic site III in common. Existing vaccines typically comprise various forms of the Rabies G protein (e.g. subunit, nucleic acids encoding the G protein, inactivated, recombinant, and the like).
One drawback of many existing vaccines is storage stability. One possible solution to this problem is to produce a “microneedle patch,” which incorporates an effective rabies antigen. A microneedle patch (FIG. 1) contains an array of micron-scale, solid needles, which encapsulate vaccine in a water-soluble matrix (see e.g. U.S. Pat. No. 7,918,814, U.S. Pat. No. 8,257,324, U.S. Pat. No. 8,636,713 and US 2008/0213461, each to Prausnitz & the Georgia Tech Research Corporation, and incorporated into this disclosure, by reference, in their entirety). Within seconds of being applied, the microneedles puncture the skin, can separate from the patch, and can become embedded within the skin where they can dissolve. In the process, the microneedles can deliver the encapsulated vaccine without producing sharps waste.
An ideal rabies vaccine should 1) be safe, inexpensive and easy to formulate, 2) reduce the amount of antigen dose required to achieve effective protection, and 3) be stable at ambient temperature for deployment to the developing countries. However, until this disclosure, it was not known whether Rabies vaccine could be formulated into safe, effective and stable microneedle formulations. Moreover, it was not predictable whether such a microneedle formulation could be used to elicit a safe and protective immune response against subsequent virulent rabies virus challenge.